U.S. patent number 5,341,243 [Application Number 07/885,658] was granted by the patent office on 1994-08-23 for zoom lens of rear focus type.
This patent grant is currently assigned to Canon Kabushiki Kaisha. Invention is credited to Kenichi Kimura, Atsushi Okuyama, Saburo Sugawara.
United States Patent |
5,341,243 |
Okuyama , et al. |
August 23, 1994 |
**Please see images for:
( Certificate of Correction ) ** |
Zoom lens of rear focus type
Abstract
A zoom lens of the rear focus type is disclosed, comprising
first, second, third and fourth lens units of positive, negative,
positive and positive refractive powers in this order from the
object side, zooming from the wide-angle end to the telephoto end
being performed by moving the second lens unit toward the image
side, compensation for the image shift and focusing being performed
by moving the fourth lens unit, and the zoom lens satisfying the
following conditions: where Fb is a back focal distance in the
wide-angle end, FW is the shortest focal length of the entire lens
system, and f3,4 is a composite focal length of the third and
fourth lens units.
Inventors: |
Okuyama; Atsushi (Tokyo,
JP), Kimura; Kenichi (Kanagawa, JP),
Sugawara; Saburo (Kanagawa, JP) |
Assignee: |
Canon Kabushiki Kaisha (Tokyo,
JP)
|
Family
ID: |
26486434 |
Appl.
No.: |
07/885,658 |
Filed: |
May 19, 1992 |
Foreign Application Priority Data
|
|
|
|
|
Jun 4, 1991 [JP] |
|
|
3-159724 |
Jun 4, 1991 [JP] |
|
|
3-159725 |
|
Current U.S.
Class: |
359/687;
359/684 |
Current CPC
Class: |
G02B
15/144113 (20190801) |
Current International
Class: |
G02B
15/163 (20060101); G02B 15/173 (20060101); G02B
015/14 () |
Field of
Search: |
;359/677,684,687 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
58-136012 |
|
Aug 1983 |
|
JP |
|
58-160913 |
|
Sep 1983 |
|
JP |
|
62-24213 |
|
Feb 1987 |
|
JP |
|
63-44614 |
|
Feb 1988 |
|
JP |
|
Primary Examiner: Sugarman; Scott J.
Attorney, Agent or Firm: Fitzpatrick, Cella, Harper &
Scinto
Claims
What is claimed is:
1. A zoom lens of the rear focus type comprising: from front to
rear, a first lens unit of positive refractive power, a second lens
unit of negative refractive power, a third lens unit of positive
refractive power and a fourth lens unit of positive refractive
power, zooming from a wide-angle end to a telephoto end being
performed by moving said first lens unit toward an object side and
said second lens unit toward an image side, while shift of an image
plane resulting from the zooming is simultaneously compensated for
by moving said fourth lens unit, and focusing from an infinitely
distant object to a closest object being performed by moving said
fourth lens unit toward the object side, wherein, letting the focal
length of the i-th lens unit be denoted by fi, the shortest focal
length of the entire lens system by FW, the longest focal length of
the entire lens system by FT, an interval between principal points
of said third and fourth lens units in the telephoto end when
focusing on an infinitely distant object by e3T, and a paraxial
back focal distance in the telephoto end by FBT, the following
conditions are satisfied: ##EQU6##
2. A zoom lens of the rear focus type according to claim 1,
satisfying the following condition:
where M1 and M2 are the amounts of movement during zooming of said
first and second lens units, respectively.
3. A zoom lens of the rear focus type according to claim 1,
satisfying the following condition: ##EQU7## where .beta.2T is a
lateral magnification of said second lens unit in the telephoto
end, and z is a zoom ratio of the entire lens system.
4. A zoom lens of the rear focus type according to claim 1,
satisfying the following condition:
where f2 is the focal length of said second lens unit.
5. A zoom lens of the rear focus type according to claim 1, wherein
said third lens unit includes at least one positive lens of
meniscus shape having an aspheric surface convex toward the object
side.
6. A zoom lens of the rear focus type comprising, from front to
rear, a first lens unit of positive refractive power, a second lens
unit of negative refractive power, a third lens unit of positive
refractive power and a fourth lens unit of positive refractive
power, zooming from a wide-angle end to a telephoto end being
performed by moving said second lens unit toward an image side,
while the shift of an image plane resulting from the zooming is
compensated for by moving said fourth lens unit, and focusing being
performed by moving said fourth lens unit, wherein, letting a
composite focal length of said third and fourth lens units in the
wide-angle end be denoted by f3,4, the focal length of the entire
lens system in the wide-angle end by FW, and a back focal distance
in the wide-angle end by Fb, the following conditions are
satisfied:
7. A zoom lens of the rear focus type according to claim 6,
satisfying the following conditions: ##EQU8## where f2 is the focal
length of said second lens unit, .beta.2T is the image
magnification of said second lens unit, FT is the longest focal
length of the entire lens system, and z is a zoom ratio.
8. A zoom lens of the rear focus type according to claim 7,
satisfying the following condition: ##EQU9## where e3W is an
interval between principal points of said third and fourth lens
unit in the wide-angle end.
9. A zoom lens of the rear focus type according to claim 8, wherein
said third lens unit has at least one aspheric surface of such
shape that a positive refractive power gets progressively weaker
from the center of the lens surface to its marginal zone.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to zoom lenses of the rear focus type and,
more particularly, to zoom lenses of the rear focus type which have
as high a range of magnification as 8 and as large an aperture
ratio as 1.6-2.4 in F-number with a short total length, and are to
be used in photographic cameras, video cameras, or cameras for
broadcasting.
2. Description of the Related Art
In the field of zoom lenses for photographic cameras or video
cameras, an increasing number of ones in which a lens unit other
than the first, when counted from the object side, is moved to
perform focusing, or which employ the so-called rear focus type,
have been proposed.
In general, the use of the rear focus type decreases the effective
diameter of the first lens unit of the zoom lens from that of a
zoom lens which performs focusing by moving the first lens unit.
This makes it easier to minimize the bulk and size of the entirety
of the lens system. Also, close-up photography, particularly
supercloseup photography, becomes easy to carry out. Further,
because the focusing lens unit is relatively small in size and
light in weight, a weak driving power for that lens unit is
sufficient. This leads to a possibility of performing rapid
focusing.
Of the zoom lenses of the rear focus type having such advantages,
for example, Japanese Laid-Open Patent Application No. Sho 63-44614
shows a so-called 4-unit zoom lens comprising, in the order from
the object side, a first lens unit of positive refractive power, a
second lens unit of negative refractive power for varying the
magnification, a third lens unit of negative refractive power for
compensating for the image shift with zooming, and a fourth lens
unit of positive refractive power, wherein the third lens unit is
made to move for focusing purposes. However, this zoom lens has to
create a space that allows the third lens unit to move and there is
a tendency to increase the total length of the entire lens
system.
In Japanese Laid-Open Patent Application No. Sho 58-136012, the
zooming section is constructed with three or more lens units, of
which some are made movable for focusing.
In Japanese Laid-Open Patent Applications No. Sho 62-247316 and No.
Sho 62-24213, the zoom lens has four lens units, i.e., a first lens
unit, when counted from the object side, of positive refractive
power, a second lens unit of negative refractive power, a third
lens unit of positive refractive power and a fourth lens unit of
positive refractive power, wherein the image magnification is
varied by moving the second lens unit, and compensation for image
shift and focusing are performed by moving the fourth lens
unit.
In Japanese Laid-Open Patent Application No. Sho 58-160913, there
are four lens units, i.e., the first lens unit, when counted from
the object side, of positive refractive power, the second lens unit
of negative refractive power, the third lens unit of positive
refractive power and the fourth lens unit of positive refractive
power, the first and second lens units are moved to vary the
magnification, while the fourth lens unit is simultaneously moved
to compensate for the image shift. Of these lens units, one or two
or more lens units are moved to effect focusing.
The related art to the present invention is mentioned in U.S. Pat.
No. 5,009,492 and U.S. patent application Ser. No. 534,241 filed on
Jun. 7, 1990.
Recently, in the field of video cameras, the trend to minimize the
size of the image sensor in the solid-state form (CCD) is
advancing. For example, in place of the conventional 1/4 in. or 1/2
in. solid-state image sensing element a smaller size, namely, 1/3
in. or 1/4 in., of image sensing element is being used. In
addition, a zoom lens to be used is required to be of a smaller
size according to the small-sized image sensing element.
Also, in the photographic lens adapted to be used in the video
camera, the distance from the last lens surface to the surface of
the image sensing element, i.e., the back focal distance, must be
made relatively long. Otherwise, dust or fine foreign particles on
the last lens surface would cast their shadow on the image
receiving surface, giving bad influence to the image.
However, if, as the design for the zoom lens that is adapted to be
used with, for example, the 1/2 in. image sensor, is applied to one
which is to be used with the 1/4 in. image sensor, the size of that
zoom lens is merely scaled down, the back focal distance gets
shorter in proportion (to 1/2). Then, the shadow against the
foreign particles or the like on the last lens surface is caused to
appear on the image receiving surface, thus giving rise to a
problem of lowering the image quality. For this reason, even the
reduction of the size of the image sensor leads to a requirement
that, as far as the zoom lens for the video camera is concerned,
the back focal distance be made longer than a predetermined
value.
In general, if the zoom lens of the rear focus type is employed,
the bulk and size of the entire lens system is minimized and rapid
focusing becomes possible.
On the other hand, however, the range of variation of aberrations
with focusing is caused to increase. So, a problem arises in that
it becomes very difficult to obtain a high optical performance
throughout the entire range of distances of objects from an
infinitely distant object to an object at the minimum distance,
while still maintaining the minimization of the bulk and size of
the entire lens system to be achieved. Particularly, with respect
to a large relative aperture, high range zoom lens, the problem of
maintaining good stability of high optical performance throughout
the entire zooming range and throughout the entire focusing range
becomes very serious.
SUMMARY OF THE INVENTION
The present invention, while employing the rear focus type,
achieves an increase of the aperture ratio and an extension of the
range of variation of the magnification. It is, therefore, an
object of the invention to provide a zoom lens of the rear focus
type which minimizes in the bulk and size of the entire lens
system, while still permitting good stability of optical
performance throughout the range of variation of the magnification
from the wide-angle end to the telephoto end, i.e., the entire
zooming range, and throughout the range of object distances from an
infinitely distant object to a closest object, i.e., the entire
focusing range, to be achieved and which has a desired certain back
focal distance.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagram for explaining the paraxial refractive power
arrangement of the invention.
FIG. 2 is a longitudinal section view of a numerical example 1 of a
zoom lens of the invention.
FIG. 3 is a longitudinal section view of a numerical example 2 of a
zoom lens of the invention.
FIG. 4 is a longitudinal section view of a numerical example 3 of a
zoom lens of the invention.
FIGS. 5A-5C show graphs of the various aberrations of the numerical
example 1 of the invention in the wideangle end.
FIGS. 6A-6C show graphs of the various aberrations of the numerical
example 1 of the invention in an intermediate position.
FIGS. 7A-7C show graphs of the various aberrations of the numerical
example 1 of the invention in the telephoto end.
FIGS. 8A-8C show graphs of the various aberrations of the numerical
example 2 of the invention in the wideangle end.
FIGS. 9A-9C show graphs of the various aberrations of the numerical
example 2 of the invention in an intermediate position.
FIGS. 10A-10C show graphs of the various aberrations of the
numerical example 2 of the invention in the telephoto end.
FIGS. 11A-11C show graphs of the various aberrations of the
numerical example 3 of the invention in the wideangle end.
FIGS. 12A-12C show graphs of the various aberrations of the
numerical example 3 of the invention in an intermediate
position.
FIGS. 13A-13C show graphs of the various aberrations of the
numerical example 3 of the invention in the telephoto end.
FIG. 14 is a longitudinal section view of a numerical example 4 of
a zoom lens of the invention.
FIG. 15 is a longitudinal section view of a numerical example 5 of
a zoom lens of the invention.
FIG. 16 is a longitudinal section view of a numerical example 6 of
a zoom lens of the invention.
FIGS. 17A-17C show graphs of the various aberrations of the
numerical example 4 of the invention in the wideangle end.
FIGS. 18A-18C show graphs of the various aberrations of the
numerical example 4 of the invention in an intermediate
position.
FIGS. 19A-19C show graphs of the various aberrations of the
numerical example 4 of the invention in the telephoto end.
FIGS. 20A-20C show graphs of the various aberrations of the
numerical example 5 of the invention in the wideangle end.
FIGS. 21A-21C show graphs of the various aberrations of the
numerical example 5 of the invention in an intermediate
position.
FIGS. 22A-22C show graphs of the various aberrations of the
numerical example 5 of the invention in the telephoto end.
FIGS. 23A-23C show graphs of the various aberrations of the
numerical example 6 of the invention in the wideangle end.
FIGS. 24A-24C show graphs of the various aberrations of the
numerical example 6 of the invention in an intermediate
position.
FIGS. 25A-25C show graphs of the various aberrations of the
numerical example 6 of the invention in the telephoto end.
In the diagram, the sectional views and the graphs of the various
aberrations of the zoom lenses described above, L1 represents the
first lens unit, L2 the second lens unit, L3 the third lens unit,
L4 the fourth lens unit, SP the aperture stop, .DELTA. S the
sagittal image surface, and .DELTA. M the meridional image
surface.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 1 is a schematic diagram illustrating the paraxial refractive
power arrangement of an embodiment of a zoom lens of the rear focus
type according to the invention. FIGS. 2 to 4 and FIGS. 14 to 16
are longitudinal section views of the numerical examples 1 to 6 of
the zoom lenses to be described later.
In the drawings, L1 is a first lens unit of positive refractive
power, L2 is a second lens unit of negative refractive power, L3 is
a third lens unit of positive refractive power and L4 is a fourth
lens unit of positive refractive power. SP is an aperture stop
arranged in front of the third lens unit L3.
When zooming from the wide-angle end to the telephoto end, the
second lens unit is moved to the image side as shown by an arrow,
while the shift of an image plane with zooming is compensated for
by moving the fourth lens unit.
Further, the fourth lens unit is axially moved to effect focusing.
That is, the rear focus type is employed. So, the fourth lens unit
moves along a locus shown by a solid line curve 4a in FIG. 1 for
focusing on an infinitely distant object, or a dashed line curve 4b
for focusing on a closest object, when compensating for the image
shift during zooming from the wide-angle end to the telephoto end.
Incidentally, the first and third lens units in this embodiment
remain stationary during zooming and focusing.
In the present embodiment, the compensating provision for the shift
of the image plane resulting from the variation of the focal length
and the focusing provision are made in the fourth lens unit.
Particularly, the locus of the movement with zooming from the
wide-angle end to the telephoto end is made convex toward the
object side as shown by the curves 4a and 4b in FIG. 1. These
afford an efficient utilization of the space between the third and
fourth lens units, thus advantageously achieving a shortening of
the total length of the entire lens system.
In the present embodiment, focusing from an infinitely distant
object to a closest object at, for example, the telephoto end is
performed by moving the fourth lens unit forward as shown by a
straight line arrow 4c in FIG. 1.
A feature of the present embodiment is that, as compared with the
conventional 4-unit zoom lens which has the focusing provision made
in the first lens unit, the effective diameter of the first lens
unit is prevented from largely increasing, by employing the rear
focus type in such a way as described above.
Another feature is that the aperture stop is positioned just before
the third lens unit to lessen the variation of aberrations due to
the movable lens units, and the separations between those of the
lens units which lie ahead of the aperture stop are shortened to
facilitate the shortening of the diameter of the front lens
members.
Still other features are that, letting the composite focal length
of the third and fourth lens units in the wide-angle end be denoted
by f3,4, the shortest focal length of the entire lens system by FW,
and the back focal distance in the wide-angle end by Fb, the
following conditions are satisfied:
By setting forth the refractive powers for the lens units as
specified above, a high range zoom lens is obtained in which the
bulk and size of the entire lens system are minimized in such a
manner that a predetermined value of the back focal distance is
secured, while still permitting good stability of optical
performance to be maintained throughout the entire zooming range
and, further, throughout the entire focusing range.
The technical significance of each of the abovedescribed conditions
is explained below.
The inequality of condition (1) is concerned with the ratio of the
back focal distance to the shortest focal length of the entire lens
system and has an aim chiefly to obtain a predetermined back focal
distance with the reduction of the bulk and size of the entire lens
system to a minimum. When the back focal distance is too short as
exceeding the lower limit of the condition (1), the shadows against
the foreign particles on the last lens surface become appreciable
at the surface of the image sensor, thus lowering the image
quality.
The inequalities of condition (2) are concerned with the ratio of
the back focal distance to the composite focal length of the third
and fourth lens units in the wide-angle end and have an aim chiefly
to obtain a certain amount of the back focal distance in such a
manner that the variation of aberrations is lessened. When the
composite positive refractive power of the third and fourth lens
units is too weak as exceeding the lower limit of the condition
(2), the back focal distance is caused to shorten. As has been
described above, therefore, the shadows of the foreign particles on
the last lens surface become appreciable in the image. Thus a bad
influence is given to the image quality. When the composite
refractive power of the third and fourth lens units is too strong
as exceeding the upper limit, particularly when the refractive
power of the fourth lens unit is too strong, variation of the
aberrations with zooming and focusing becomes objectionably
large.
The zoom lens of the rear focus type according to the invention is
achieved by satisfying the abovedescribed various conditions. To
obtain a better optical performance throughout the entire zooming
range and throughout the entire focusing range with the bulk and
size of the entire lens system to the minimum, however, it is
preferred to satisfy the following conditions i) to iii): ##EQU1##
where f2 is the focal length of the second lens unit, .beta.2T is
the image magnification of the second lens unit in the telephoto
end, FT is the longest focal length of the entire lens system, and
z is the zoom ratio.
The inequalities of condition (3) have an aim to fulfill the
requirements of suppressing the variation of the aberrations with
zooming and of advantageously shortening the total length of the
entire lens system. When the negative refractive power of the
second lens unit is too weak as exceeding the upper limit, the
required total movement for a predetermined zoom ratio of the
second lens unit has to be increased. In turn, the total length of
the entire lens system becomes longer. When the negative refractive
power of the second lens unit is too strong as exceeding the lower
limit, the Petzval sum increases in the negative sense. So, the
curvature of field becomes large and the coma becomes difficult to
correct well. Also, the variation, too, of the aberrations with
zooming increases objectionably.
When the absolute value of the magnifying power of the second lens
unit in the telephoto end is too small as exceeding the lower limit
of the condition (4), the required total movement for a
predetermined zoom ratio of the second lens unit is caused to
increase. In turn, the total length of the entire lens system
becomes long. When the magnifying power is too large as exceeding
the upper limit, the sensitivity on the telephoto side becomes
large and the amount of accompanying movement of the fourth lens
unit with zooming increases. Further, the back focal distance
becomes short. So, it is no good. ##EQU2## where e3W is the
interval between the principal points of the third and fourth lens
units in the wide-angle end.
When the principal point interval is too short as exceeding the
lower limit of the condition (5), as the fourth lens unit is used
in focusing, the space in which the fourth lens unit can move
becomes small. When the principal point interval is too long as
exceeding the upper limit, it becomes difficult to secure the back
focal distance at a predetermined value.
iii) The aforesaid third lens unit has at least one aspheric
surface of such shape that the positive refractive power gets
progressively weaker from the center of the area of the lens
surface to the marginal zone.
Owing to this aspheric surface, the number of lens elements of the
third lens unit is lessened to shorten the total length of the
entire lens system, while still preserving the high optical
performance throughout the entire zooming range.
Incidentally, in the numerical examples 2 and 3 to be described
later, of the lens elements, a bi-convex lens is provided with the
aspheric surface at the object side to thereby correct the various
aberrations in good balance.
Next, numerical examples 1 to 3 of the invention are shown. In the
numerical data for the examples 1 to 3, Ri is the i-th lens surface
when counted from the object side, Di is the i-th lens thickness or
air separation, and Ni and .upsilon.i are respectively the
refractive index and Abbe number of the glass of the i-th lens
element.
R24 and R25 of the numerical example 1 and R22 and R23 of the
numerical examples 2 and 3 denote face plates or like glass
blocks.
The shape of the aspheric surface is expressed in coordinates with
an X-axis in the axial direction and an H-axis in the direction
perpendicular to the optical axis, the direction in which light
advances being taken as positive, by the following equation:
##EQU3## where R is the radius of the osculating sphere and A, B, C
and D are the aspheric coefficients.
The values of the factors in the conditions for the numerical
examples 1 to 3 are listed in Table-1.
______________________________________ Numerical Example 1: (FIGS.
2, 5A-5C, 6A-6C, and 7A-7C) F = 1-7.6 FNO = 1:1.65-2.3 2.omega. =
48.8.degree.-6.8.degree. ______________________________________ R1
= 7.869 D1 = 0.138 N1 = 1.80518 .nu. 1 = 25.4 R2 = 3.741 D2 = 0.759
N2 = 1.51633 .nu. 2 = 64.1 R3 = -12.767 D3 = 0.037 R4 = 3.112 D4 =
0.463 N3 = 1.60311 .nu. 3 = 60.7 R5 = 11.504 D5 = Variable R6 =
9.688 D6 = 0.111 N4 = 1.69680 .nu. 4 = 55.5 R7 = 1.091 D7 = 0.412
R8 = -1.482 D8 = 0.111 N5 = 1.69680 .nu. 5 = 55.5 R9 = 1.567 D9 =
0.333 N6 = 1.84666 .nu. 6 = 23.9 R10 = -13.469 D10 = Variable R11 =
Stop D11 = 0.208 R12 = 27.330 D12 = 0.463 N7 = 1.63854 .nu. 7 =
55.4 R13 = -2.140 D13 = 0.084 R14 = -1.586 D14 = 0.111 N8 = 1.80518
.nu. 8 = 25.4 R15 = -2.890 D15 = 0.027 R16 = 2.389 D16 = 0.240 N9 =
1.51633 .nu. 9 = 64.1 R17 = 8.012 D17 = Variable R18 = 5.617 D18 =
0.111 N10 = 1.84666 .nu. 10 = 23.9 R19 = 2.449 D19 = 0.148 R20 =
14.250 D20 = 0.407 N11 = 1.60311 .nu. 11 = 60.7 R21 = -2.690 D21 =
0.027 R22 = 2.808 D22 = 0.370 N12 = 1.51633 .nu. 12 = 64.1 R23 =
-11.298 D23 = 0.740 R24 = .infin. D24 = 0.740 N13 = 1.51633 .nu. 13
= 64.1 R25 = .infin. ______________________________________
Variable Focal Length Separation 1.00 4.24 7.60
______________________________________ D5 0.26 2.21 2.77 D10 2.67
0.72 0.17 D17 0.82 0.42 1.00
______________________________________
______________________________________ Numerical Example 2: (FIGS.
3, 8A-8C, 9A-9C, and 10A-10C) F = 1-7.6 FNO = 1:1.65-2.43 2.omega.
= 48.8.degree.-6.8.degree. ______________________________________
R1 = 6.511 D1 = 0.138 N1 = 1.80518 .nu. 1 = 25.4 R2 = 3.126 D2 =
0.722 N2 = 1.51633 .nu. 2 = 64.1 R3 = -12.832 D3 = 0.037 R4 = 2.772
D4 = 0.490 N3 = 1.60311 .nu. 3 = 60.7 R5 = 12.291 D5 = Variable R6
= 10.212 D6 = 0.092 N4 = 1.69680 .nu. 4 = 55.5 R7 = 0.920 D7 =
0.353 R8 = -1.259 D8 = 0.092 N5 = 1.69680 .nu. 5 = 55.5 R9 = 1.242
D9 = 0.259 N6 = 1.84666 .nu. 6 = 23.9 R10 = -9.426 D10 = Variable
R11 = Stop D11 = 0.208 R12 = aspheric D12 = 0.428 N7 = 1.60311 .nu.
7 = 60.7 surface R13 = -2.648 D13 = 0.055 R14 = -2.064 D14 = 0.102
N8 = 1.80518 .nu. 8 = 25.4 R15 = -4.377 D15 = Variable R16 = 8.928
D16 = 0.111 N9 = 1.84666 .nu. 9 = 23.9 R17 = 2.438 D17 = 0.148 R18
= 20.913 D18 = 0.287 N10 = 1.60311 .nu. 10 = 60.7 R19 = -2.995 D19
= 0.027 R20 = 2.728 D20 = 0.444 N11 = 1.51633 .nu. 11 = 64.1 R21 =
-3.300 D21 = 0.740 R22 = .infin. D22 = 0.740 N12 = 1.51633 .nu. 12
= 64.1 R23 = .infin. ______________________________________
Variable Focal Length Separation 1.00 4.10 7.60
______________________________________ D5 0.21 1.84 2.35 D10 2.37
0.74 0.23 D15 0.87 0.40 1.08
______________________________________
Values of the Aspheric Coefficients:
______________________________________ R = 2.322 A = 0 B = -2.196
.times. 10.sup.-2 C = 1.238 .times. 10.sup.-2 D = -7.496 .times.
10.sup.-3 ______________________________________
______________________________________ Numerical Example 3: (FIGS.
4, 11A-11C, 12A-12C, and 13A-13C) F = 1-7.6 FNO = 1:1.65-2.43
2.omega. = 48.8.degree.-6.8.degree.
______________________________________ R1 = 7.446 D1 = 0.138 N1 =
1.80518 .nu. 1 = 25.4 R2 = 3.672 D2 = 0.574 N2 = 1.51633 .nu. 2 =
64.1 R3 = -13.780 D3 = 0.037 R4 = 3.219 D4 = 0.416 N3 = 1.60311
.nu. 3 = 60.7 R5 = 11.755 D5 = Variable R6 = 4.976 D6 = 0.111 N4 =
1.69680 .nu. 4 = 55.5 R7 = 1.101 D7 = 0.423 R8 = -1.492 D8 = 0.111
N5 = 1.69680 .nu. 5 = 55.5 R9 = 1.442 D9 = 0.259 N6 = 1.84666 .nu.
6 = 23.9 R10 = 129.653 D10 = Var- iable R11 = Stop D11 = 0.200 R12
= aspheric D12 = 0.463 N7 = 1.60311 .nu. 7 = 60.7 surface R13 =
-3.189 D13 = 0.064 R14 = -2.292 D14 = 0.111 N8 = 1.80518 .nu. 8 =
25.4 R15 = -6.099 D15 = Var- iable R16 = 4.707 D16 = 0.120 N9 =
1.84666 .nu. 9 = 23.9 R17 = 2.436 D17 = 0.168 R18 = 17602.765 D18 =
0.287 N10 = 1.60311 .nu. 10 = 60.7 R19 = -2.688 D19 = 0.027 R20 =
2.698 D20 = 0.351 N11 = 1.51633 .nu. 11 = 64.1 R21 = -5.820 D21 =
0.740 R22 = .infin. D22 = 0.740 N12 = 1.51633 .nu. 12 = 64.1 R23 =
.infin. ______________________________________ Variable Focal
Length Separation 1.00 4.40 7.60
______________________________________ D5 0.18 2.21 2.78 D10 2.80
0.78 0.21 D15 0.97 0.44 0.97
______________________________________
Values of the Aspheric Coefficients:
______________________________________ R = 2.250 A = 0 B = -1.715
.times. 10.sup.-2 C = 3.506 .times. 10.sup.-3 D = 3.715 .times.
10.sup.-5 ______________________________________
TABLE 1 ______________________________________ Numerical Example
Condition 1 2 3 ______________________________________ (1)
.vertline.Fb/FW.vertline. 2.30 2.30 2.44 (2)
.vertline.Fb/f3,4.vertline. 0.99 0.98 1.04 ##STR1## 0.39 0.34 0.39
##STR2## 1.20 1.22 1.00 ##STR3## 0.65 0.70 0.73
______________________________________
Next explanation is given to another embodiment of the zoom lens as
considered from another standpoint to be suited when in application
to the 1/4 in. image sensor.
The zoom lens of the rear focus type of the invention comprises,
from front to rear, a first lens unit of positive refractive power,
a second lens unit of negative refractive power, a stop, a third
lens unit of positive refractive power and a fourth lens unit of
positive refractive power, the first lens unit being moved toward
the object side and the second lens unit being moved toward the
image side when zooming from the wideangle end to the telephoto
end, while the fourth lens unit is simultaneously moved to
compensate for the image shift resulting from the variation of the
image magnification, wherein the fourth lens unit is moved toward
the object side to effect focusing from an infinitely distant
object to a closest object, and, letting the focal length of the
i-th lens unit be donated by fi, the shortest focal length of the
entire lens system by FW, the longest focal length of the entire
lens system by FT, the interval between the principal points of the
third and fourth lens units in the telephoto end with an infinitely
distant object in focus by e3T, and the paraxial back focal
distance in the telephoto end by FBT, the following conditions are
satisfied:
______________________________________ 0.32 < FBT/FT < 0.50 .
. . (6) 2 < f3/f4 < 9 . . . (7) 2 < e3T/FW < 5 . . .
(8) ______________________________________
The technical significance of each of the above-described
conditions is explained below.
The inequalities of condition (6) are concerned with the ratio of
the back focal distance to the longest focal length of the entire
lens system and have an aim chiefly to obtain a predetermined back
focal distance in such a manner that the bulk and size of the
entire lens system are reduced. When the back focal distance is too
short as exceeding the lower limit of the condition (6), the
shadows against the foreign particles on the last lens surface
become appreciable on the surface of the image sensor, lowering the
image quality. When the back focal distance is too long as
exceeding the upper limit, as so much unnecessary space arises
between the lens system and the image sensor, the size of the
entire lens system is caused to increase objectionably.
The inequalities of condition (7) are concerned with the ratio of
the focal lengths of the third and fourth lens units and have an
aim chiefly to effectively obtain a certain value of the back focal
distance. When the positive refractive power of the third lens unit
is too strong as exceeding the lower limit of the condition (7),
the back focal distance becomes too short and the refractive power
of the fourth lens unit becomes too weak as compared with the third
lens unit, causing the amount of focusing movement of the fourth
lens unit to increase largely. Thus, the size of the lens system as
a whole comes to increase. When the refractive power of the third
lens unit is too weak as exceeding the upper limit, the back focal
distance becomes too long and the refractive power of the fourth
lens unit comes to be strong as compared with the third lens unit.
Thus, the variation of aberrations with focusing increases
objectionably.
The inequalities of condition (8) are concerned with the interval
between the principal points of the third and fourth lens units in
the telephoto end and have an aim chiefly to preserve the optical
performance on the telephoto side. When the principal point
interval is too short as exceeding the lower limit of the condition
(8), the available range of movement of the fourth lens unit during
focusing becomes too narrow. So, it becomes difficult to focus on a
closest object. When the principal point interval is too long as
exceeding the upper limit, an unnecessary space arises, increasing
the size of the entire lens system objectionably.
The zoom lens of the rear focus type according to the invention is
achieved by satisfying the abovedescribed various conditions.
However, to facilitate fulfillment of the requirements of reducing
the bulk and size of the entire lens system and of improving the
optical performance throughout the entire zooming range and
throughout the entire focusing range, it is preferred to satisfy
the following additional conditions iv) to vii):
iv)
where M1 and M2 are the amounts of movement during zooming of the
first and second lens units, respectively.
When the movement of the second lens unit is far larger than the
movement of the first lens unit as exceeding the lower limit of the
condition (9), the size of the entire lens system comes to be
large. Conversely when the movement of the first lens unit is far
larger as exceeding the upper limit, the structure of a mechanism
for operatively connecting the first and second lens units becomes
complicated. In addition, the locus of movement of the fourth lens
unit for compensating for the image shift with zooming becomes so
steep that the difficulty of drive control by the actuator
increases objectionably. ##EQU4## where .beta.2T is the lateral
magnification of the second lens unit in the telephoto end and z is
the zoom ratio of the entire lens system.
When the lateral magnification .beta.2T is too large as exceeding
the upper limit of the condition (10), the locus of movement of the
fourth lens unit becomes steep likewise as described in connection
with the condition (9). When the lower limit is exceeded, the locus
of movement of the fourth lens unit swells largely toward the
object side in the intermediate zooming positions. Therefore, the
separation between the third and fourth lens units has to be
increased. As a result, the size of the entire lens system is
increased objectionably.
vi)
where f2 is the focal length of the second lens unit.
When the refractive power of the second lens unit is too weak as
exceeding the upper limit of the condition (11), the required total
zooming movement for a predetermined zoom ratio of the second lens
unit has to be increased. Thus, the total length of the entire lens
system becomes long. When the refractive power of the second lens
unit is too strong as exceeding the lower limit, this leads to an
increase in the refractive powers of the other lens units. From the
standpoint of the aberration correction, the number of lens
elements of each unit has to be increased. So, in effect, the total
length of the entire lens system becomes long. Also, the locus of
movement of the fourth lens unit for compensating for the image
shift with zooming becomes so steep that the difficulty of driving
control by the actuator increases objectionably.
vii) The third lens unit has at least one meniscusshaped positive
lens having an aspheric surface convex toward the object side.
In the present embodiment, the second lens unit of negative
refractive power produces a diverging light beam, which passes
through the third lens unit without being much refracted because
the positive power of the third lens unit is relatively weak. With
this light beam, the various aberrations are corrected in good
balance by the aspheric meniscus lens convex toward the object
side.
Incidentally, in numerical examples to be described later, the
third lens unit is constructed with either a negative lens of
meniscus shape convex toward the object side and a positive lens of
meniscus shape convex toward the object side and having an aspheric
surface, totaling two lenses, or a positive lens of meniscus shape
convex toward the object side and having an aspheric surface,
totaling only one lens.
Next, numerical Examples 4 to 6 of the invention are shown. In the
numerical data of the examples 4 to 6, Ri is the radius of
curvature of the i-th lens surface when counted from the object
side, Di is the i-th lens thickness or air separation and Ni and
.upsilon.i are respectively the refractive index and Abbe number of
the glass of the i-th lens element.
R23 and R24 of the numerical example 4 and R21 and R22 of the
numerical examples 5 and 6 denote face plates or like glass
blocks.
The shape of the aspheric surface is expressed in coordinates with
an X-axis in the axial direction and an H-axis in the direction
perpendicular to the optical axis, the direction in which light
advances being taken as positive, by the following equation:
##EQU5## where R is the radius of the osculating sphere and A, B,
C, D and E are the aspheric coefficients.
Also, the values of the factors in the conditions (6) to (11) for
the numerical examples 4 to 6 are listed in Table-2.
______________________________________ Numerical Example 4: (FIGS.
14, 17A-17C, 18A-18C, and 19A-19C) F = 1-2.58-7.60 FNO =
1:1.45-1.52-1.80 2.omega. = 94.9.degree.-18.7.degree .-6.4.degree.
______________________________________ R1 = 10.079 D1 = 0.226 N1 =
1.80518 .nu. 1 = 25.4 R2 = 4.786 D2 = 0.905 N2 = 1.51633 .nu. 2 =
64.1 R3 = -33.682 D3 = 0.037 R4 = 4.638 D4 = 0.641 N3 = 1.65844
.nu. 3 = 50.9 R5 = 20.641 D5 = Variable R6 = 9.579 D6 = 0.132 N4 =
1.80610 .nu. 4 = 40.9 R7 = 1.124 D7 = 0.455 R8 = -1.667 D8 = 0.132
N5 = 1.51742 .nu. 5 = 52.4 R9 = 1.667 D9 = 0.396 N6 = 1.80518 .nu.
6 = 25.4 R10 = -8.681 D10 = Variable R11 = Stop D11 = 0.283 R12 =
2.156 D12 = 0.132 N7 = 1.80518 .nu. 7 = 25.4 R13 = 1.626 D13 =
0.247 R14 = aspheric D14 = 0.415 N8 = 1.58313 .nu. 8 = 59.4 surface
R15 = 2.288 D15 = Variable R16 = 7.570 D16 = 0.132 N9 = 1.84666
.nu. 9 = 23.9 R17 = 2.883 D17 = 0.185 R18 = 14.840 D18 = 0.603 N10
= 1.51633 .nu. 10 = 64.1 R19 = -2.613 D19 = 0.028 R20 = 3.064 D20 =
0.830 N11 = 1.60311 .nu. 11 = 60.7 R21 = -2.766 D21 = 0.132 N12 =
1.84666 .nu. 12 = 23.9 R22 = -3.696 D22 = 0.566 R23 = .infin. D23 =
0.754 N13 = 1.51633 .nu. 13 = 64.1 R24 = .infin.
______________________________________ R14: Aspheric Surface
______________________________________ R.sub.0 = 1.4703 B = -3.5070
.times. 10.sup.-2 C = 5.3129 .times. 10.sup.-3 D = -8.9712 .times.
10.sup.-3 ______________________________________ Variable Focal
Length Separation 1.00 2.58 7.60
______________________________________ D5 0.21 2.69 4.35 D10 2.65
1.30 0.40 D15 1.17 1.01 1.61
______________________________________
______________________________________ Numerical Example 5: (FIGS.
15, 20A-20C, 21A-21C and 22A-22C) F = 1-2.58-7.60 FNO =
1:2.05-2.14-2.75 2.omega. = 94.9.degree.-18.7.degree .-6.4.degree.
______________________________________ R1 = 11.329 D1 = 0.207 N1 =
1.80518 .nu. 1 = 25.4 R2 = 4.462 D2 = 0.905 N2 = 1.51633 .nu. 2 =
64.1 R3 = -19.331 D3 = 0.037 R4 = 4.131 D4 = 0.641 N3 = 1.65844
.nu. 3 = 50.9 R5 = 18.940 D5 = Variable R6 = 7.189 D6 = 0.132 N4 =
1.80610 .nu. 4 = 40.9 R7 = 0.905 D7 = 0.380 R8 = -1.352 D8 = 0.132
N5 = 1.51742 .nu. 5 = 52.4 R9 = 1.352 D9 = 0.396 N6 = 1.80518 .nu.
6 = 25.4 R10 = -6.198 D10 = Variable R11 = Stop D11 = 0.283 R12 =
aspheric D12 = 0.377 N7 = 1.58313 .nu. 7 = 59.4 surface R13 = 1.851
D13 = Variable R14 = 5.722 D14 = 0.132 N8 = 1.84666 .nu. 8 = 23.9
R15 = 2.771 D15 = 0.130 R16 = 18.607 D16 = 0.396 N9 = 1.51633 .nu.
9 = 64.1 R17 = -3.162 D17 = 0.028 R18 = 2.600 D18 = 0.773 N10 =
1.60311 .nu. 10 = 60.7 R19 = -2.015 D19 = 0.132 N11 = 1.84666 .nu.
11 = 23.9 R20 = -3.283 D20 = 0.566 R21 = .infin. D21 = 0.754 N12 =
1.51633 .nu. 12 = 64.1 R22 = .infin.
______________________________________ R12: Aspheric Surface
______________________________________ R.sub.0 = 1.5581 B = -2.8641
.times. 10.sup.-2 C.sub.11 = -7.5290 .times. 10.sup.-3 D = 2.5511
.times. 10.sup.-3 ______________________________________ Variable
Focal Length Separation 1.00 2.58 7.60
______________________________________ D5 0.20 2.50 4.04 D10 2.25
1.13 0.39 D13 1.71 1.50 2.15
______________________________________
______________________________________ Numerical Example 6: (FIGS.
16, 23A-23C, 24A-24C, and 25A-25C) F = 1-2.11-7.60 FNO =
1:2.05-2.11-2.17 2.omega. = 94.9.degree.-22.8.degree .-6.4.degree.
______________________________________ R1 = 10.092 D1 = 0.207 N1 =
1.80518 .nu. 1 = 25.4 R2 = 4.425 D2 = 0.867 N2 = 1.51633 .nu. 2 =
64.1 R3 = -33.016 D3 = 0.037 R4 = 4.324 D4 = 0.660 N3 = 1.65844
.nu. 3 = 50.9 R5 = 23.297 D5 = Variable R6 = 7.913 D6 = 0.132 N4 =
1.80610 .nu. 4 = 40.9 R7 = 0.979 D7 = 0.395 R8 = -1.450 D8 = 0.132
N5 = 1.51742 .nu. 5 = 52.4 R9 = 1.450 D9 = 0.358 N6 = 1.80518 .nu.
6 = 25.4 R10 = -7.792 D10 = Variable R11 = Stop D11 = 0.283 R12 =
1.568 D12 = 0.283 N7 = 1.58313 .nu. 7 = 59.4 R13 = 2.070 D13 =
Variable R14 = 9.263 D14 = 0.132 N8 = 1.84666 .nu. 8 = 23.9 R15 =
2.830 D15 = 0.129 R16 = aspheric D16 = 0.434 N9 = 1.51633 .nu. 9 =
64.1 surface R17 = -2.768 D17 = 0.028 R18 = 2.680 D18 = 0.924 N10 =
1.60311 .nu. 10 = 60.7 R19 = -2.361 D19 = 0.132 N11 = 1.84666 .nu.
11 = 23.9 R20 = -3.437 D20 = 0.566 R21 = .infin. D21 = 0.754 D12 =
1.51633 .nu. 12 = 64.1 R22 = .infin.
______________________________________ R16: Aspheric Surface
______________________________________ R.sub.0 = 20.3984 B =
-3.3497 .times. 10.sup.-2 C = -2.1297 .times. 10.sup.-3 D = -2.4996
.times. 10.sup.-3 ______________________________________ Variable
Focal Length Separation 1.00 2.11 7.60
______________________________________ D5 0.14 2.12 4.09 D10 2.54
1.56 0.58 D13 1.68 1.49 2.06
______________________________________
TABLE 2 ______________________________________ Numerical Example
Condition 4 5 6 ______________________________________ (6) FBT/FT
0.335 0.335 0.335 (7) f3/f4 7.788 4.044 3.579 (8) e3T/FW 4.077
3.946 3.566 (9) M1/M2 0.838 1.067 1.009 ##STR4## 1.788 1.288 1.199
(11) .vertline.f2/FW.vertline. 1.547 1.320 1.358
______________________________________
According to the invention, for the four lens units, their
refractive powers are set forth, for the first, second and fourth
lens units, the moving conditions in zooming are set forth, and for
the third and fourth lens units, the refractive power ratio, among
others, are set forth, as has been described above. Along with
these, the lens configuration that the fourth lens unit is moved
during focusing is employed in order that a predetermined back
focal distance is secured despite the reduction of the bulk and
size of the entire lens system. This makes it possible to obtain a
zoom lens of the rear focus type which has, despite the increase of
the zoom ratio to 8 or thereabout, to achieve a good aberration
correction throughout the entire extended zooming range, and,
during focusing, varies the aberrations to lesser extent for a high
optical performance at an increased aperture ratio to 1.4-2.0 in
F-number.
* * * * *